The invention relates to a solder braze alloy and to a method for adjoining workpieces by soldering by means of a solder braze alloy.
Soldering is one of the most common joining techniques. However, there are still some drawbacks which militate against even more widespread use of soldering for joining workpieces.
Previously known solder braze alloys can be used to good effect only if the surfaces of the workpieces to be joined are cleaned prior to the solder braze being applied and are freed from any oxide layers present, in order to ensure good contact of the solder braze with the workpiece surfraces, and/or if a flux is used together with the solder braze. This means that the workpiece surfaces to be soldered have to undergo a laborious pretreatment and/or that the soldering operation, owing to the use of a flux additive, becomes a more complicated procedure. Furthermore there is the risk that after the soldering operation flux residues will remain on the soldered workpieces, which may lead to problems with further prcessing steps or which may impair the long-term durability of the solder braze joints. Finally, some of the fluxes used constitute health and/or environmental hazards.
Known commercial solder alloys comprising tin and/or lead and possibly silver, which can be processed at about 200xc2x0 C., have the additional drawback that many materials are not wetted by them at all or only very poorly, and that they cannot be used co join workpieces having surfaces of such poorly wettable or entirely nonwettable materials. Using classic solders of this type it is not possible, for example, to solder workpieces made of ceramic materials, since ceramic surfaces are not wetted.
In earlier attempts to overcome this drawback, titanium was added to the solders. These so-called active solders comprising a percentage of titanium as the so-called active metal exhibit considerably improved wetting even of inherently poorly wettable surfaces such as, for example, ceramic materials. A considerable drawback of these active solders, however, is that they require processing temperatures of from 600 to 900xc2x0 C. and can be processed only in a high vacuum or in pure shielding gas. The need of processing under vacuum means that the soldering process becomes very laborious; in many cases using them is out of the question. Furthermore, the high processing temperature seriously limits the choice of solderable materials.
This drawback also relates to the classic active brazes which are processed at temperatures of at least 700xc2x0 C., but in most cases above 850xc2x0 C.
A further known technique, for certain special cases, is that of eutectic copper bonding, but this is even more laborious and complicated.
DE-A 195 26 822 discloses a solder braze alloy con taining:
at least 1 wt % of an element or a mixture of elements of subgroup IVa and/or Va such as Ti, Zr, Hf, V, Nb and Ta,
at least 0,01 wt % of an element or a mixture of elements of the Lanthanide group such as cerium (preferably) and neodymium,
optionally at least 0,5 wt % silver or copper or indium or a mixture of silver and/or copper and/or indium,
optionally at least 0,01 wt % gallium,
and the remainder consists of tin or lead or a mixture of tin and lead,
and customary unavoidable impurities.
This document does not disclose to provide a remainder consisting or including the element indium. This known solder braze alloy is not sufficient to be used with temperature sensitive material. Additionally, the joining of materials subjected to higher temperatures, for example above 300xc2x0 C., in use is not possible.
It is therefore an object of the invention to propose a solder braze alloy and a method for joining workpieces by soldering by means of a solder braze alloy, the method allowing soldering technology to be used in a more versatile manner. In particular, it is the object of the invention to propose a solder braze alloy which can be processed even in oxygen-containing atmospheres, for example in air, has a relatively low processing temperature and produces good wetting even on inherently poorly wettable surfaces such as, for example, ceramic surfaces. In a development of the invention, the solder braze alloy to be proposed is to be processable without a flux.
The proposed solder braze alloys are to have liquidus temperatures which, depending on the composition, can be below or above 450xc2x0 C.
This object is achieved by a novel solder braze alloy and a method for joining workpieces by soldering by means of this novel solder braze alloy.
The novel alloy, which generally is an active solder braze alloy, is characterized in that it comprises
1-10 wt % of an element or a mixture of elements. of subgroup IVa and/or Va of the Periodic Table of the elements,
0,01-20 wt % of an element or a mixture of elements of the group of the rare earths,
0-10 wt % of silver or copper or a mixture of silver and copper,
0-50 wt % of antimony
0-5% wt % of nickel, cobalt, manganese or chromium or a mixture of two or more of the elements nickel, cobalt, manganese or chromium, and
0-10 wt % of gallium and the remainder consists of zinc, bismuth, indium or a mixture of two or more of the elements zinc, lead, tin, bismuth and indium, one of the mixture elements being zinc, bismuth or indium,
and possibly of customary impurities.
The proposed active solder braze alloy therefore consists of at least three components, namely a first component which consists of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements; a second component which consists of an element or a mixture of elements of the group of the rare earths; and of a third component making up the remainder, which predominantly consists of zinc, lead, tin, bismuth or indium or a mixture of two or more of the elements zinc, lead, tin, bismuth and indium.
Preferably, the alloy according to the invention, which can be an active solder alloy or an active braze alloy, additionally comprises a further, fourth component which consists of silver or copper or a mixture of silver and copper; and/or another further, fifth component which consists of gallium. A sixth component of antimony and a seventh component of nickel, manganese, chromium or cobalt can advantageously likewise be provided. The fourth and possibly fifth, sixth, seventh components are advantageously present in the novel alloy, but are not absolutely necessary to achieve the advantages of the invention.
The elements of subgroup IVa and/or Va of the Periodic Table of the Elements include, inter alia, the elements titanium, zirconium, hafnium, vanadium, niobium and tantalum, among which titanium is preferred. The elements of the rare earths include, inter alia, cerium, praseodymium, neodymium, gadolinium and ytterbium, among which cerium is preferred. A mixture of elements of the rare earths, cerium being the main component, is likewise preferred as the second component.